[Tbos]

From what I read on a similar post I originated, 2 things can cause this. One is related to heat causing the Filon to expand away from the cheap backing at that location. The other is due to heat and some (possibly even a small amount) moisture getting into the wall at some point and causing the same thing. Since the Filon is anchored on all 4 sides it has nowhere to go when it expands but out. Unfortunately, when it contracts it doesn't return to its original shape.


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